The fabrication processes of semiconductor devices usually include a backside metallization process, which is essential for heat dissipation, the device grounding, as well as improving the die strength. FIG. 1 is a schematic showing the backside copper structure of semiconductor devices according to conventional technologies, in which the structure sequentially comprises a substrate 101, a diffusion barrier layer 105, a stress-reducing metal layer 107, a backside metal layer 109, and an oxidation resistant layer 111. The diffusion barrier layer 105 is formed below the substrate 101. The diffusion barrier layer 105 is made of TaN, which is used mainly for preventing device damages caused by the diffusion of other metal atoms into the substrate 101. The stress-reducing metal layer 107 is formed below the diffusion barrier layer 105. The stress-reducing metal layer 107 is made of Au, which can prevent metal peeling off from the underneath structure caused by the mismatched thermal expansions/contractions in different material layers. The backside metal layer 109 is made of Cu. The backside metal layer 109 should be thick enough to support the substrate 101 for sustaining the large stress during packaging processes. A thick backside metal layer is also helpful for device heat dissipation. The oxidation resistant layer 111 is made of Au, which can prevent the oxidation of the backside metal layer 109.
However, choosing TaN for the diffusion barrier layer, Au for the stress-reducing metal layer, and Cu for the backside metal layer is not adequate for semiconductor devices that demanded for high-temperature operations. The heat dissipation and thermal resistance of semiconductor devices are important topics nowadays. A semiconductor device may be damaged by over-heating when its thermal resistance is not good enough, particularly when backside via holes with large depth to width aspect ratios are presented in the semiconductor devices. Under high temperature operations, the three-layer structure would crack or peel off, leading to poor grounding and device damages.
In view of these facts and for overcoming the drawback stated above, the present invention provides an improved structure of the backside copper metallization a fabrication method thereof for semiconductor devices that can sustain high temperature operations. The improved structure and the fabrication method thereof according to the present invention can also improve the thermal conductivity of the semiconductor chip with a lower production cost.